This invention relates generally to the field of digitally controlled printing devices, and in particular to continuous ink jet printers in which a liquid ink stream breaks into droplets, some of which are selectively deflected.
Traditionally, digitally controlled color printing capability is accomplished by one of two technologies. Both require independent ink supplies for each of the colors of ink provided. Ink is fed through channels formed in the printhead. Each channel includes a nozzle from which droplets of ink are selectively extruded and deposited upon a medium. Typically, each technology requires separate ink delivery systems for each ink color used in printing. Ordinarily, the three primary subtractive colors, i.e. cyan, yellow and magenta, are used because these colors can produce, in general, up to several million perceived color combinations.
The first technology, commonly referred to as xe2x80x9cdrop-on-demandxe2x80x9d ink jet printing, provides ink droplets for impact upon a recording surface using a pressurization actuator (thermal, piezoelectric, etc.). Selective activation of the actuator causes the formation and ejection of a flying ink droplet that crosses the space between the printhead and the print media and strikes the print media. The formation of printed images is achieved by controlling the individual formation of ink droplets, as is required to create the desired image. Typically, a slight negative pressure within each channel keeps the ink from inadvertently escaping through the nozzle, and also forms a slightly concave meniscus at the nozzle, thus helping to keep the nozzle clean.
Conventional xe2x80x9cdrop-on-demandxe2x80x9d ink jet printers utilize a pressurization actuator to produce the ink jet droplet at orifices of a print head. Typically, one of two types of actuators are used including heat actuators and piezoelectric actuators. With heat actuators, a heater, placed at a convenient location, heats the ink causing a quantity of ink to phase change into a gaseous steam bubble that raises the internal ink pressure sufficiently for an ink droplet to be expelled. With piezoelectric actuators, an electric field is applied to a piezoelectric material possessing properties that create a mechanical stress in the material causing an ink droplet to be expelled. The most commonly produced piezoelectric materials are ceramics, such as lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate.
U.S. Pat. No. 4,914,522 issued to Duffield et al., on Apr. 3, 1990 discloses a drop-on-demand ink jet printer that utilizes air pressure to produce a desired color density in a printed image. Ink in a reservoir travels through a conduit and forms a meniscus at an end of an inkjet nozzle. An air nozzle, positioned so that a stream of air flows across the-meniscus at the end of the ink nozzle, causes the ink to be extracted from the nozzle and atomized into a fine spray. The stream of air is applied at a constant pressure through a conduit to a control valve. The valve is opened and closed by the action of a piezoelectric actuator. When a voltage is applied to the valve, the valve opens to permit air to flow through the air nozzle. When the voltage is removed, the valve closes and no air flows through the air nozzle. As such, the ink dot size on the image remains constant while the desired color density of the ink dot is varied depending on the pulse width of the air stream.
The second technology, commonly referred to as xe2x80x9ccontinuous streamxe2x80x9d or xe2x80x9ccontinuousxe2x80x9d ink jet printing, uses a pressurized ink source which produces a continuous stream of ink droplets. Conventional continuous ink jet printers utilize electrostatic charging devices that are placed close to the point where a filament of working fluid breaks into individual ink droplets. The ink droplets are electrically charged and then directed to an appropriate location by deflection electrodes having a large potential difference. When no print is desired, the ink droplets are deflected into an ink capturing mechanism (catcher, interceptor, gutter, etc.) and either recycled or disposed of. When print is desired, the ink droplets are not deflected and allowed to strike a print media. Alternatively, deflected ink droplets may be allowed to strike the print media, while non-deflected ink droplets are collected in the ink capturing mechanism.
Typically, continuous ink jet printing devices are faster than droplet on demand devices and produce higher quality printed images and graphics. However, each color printed requires an individual droplet formation, deflection, and capturing system.
Conventional continuous ink jet printers utilize electrostatic charging devices and deflector plates, they require many components and large spatial volumes in which to operate. This results in continuous ink jet printheads and printers that are complicated, have high energy requirements, are difficult to manufacture, and are difficult to control. Examples of conventional continuous ink jet printers include U.S. Pat. No. 1,941,001, issued to Hansell, on Dec. 26, 1933; U.S. Pat. No. 3,373,437 issued to Sweet et al., on Mar. 12, 1968; U.S. Pat. No. 3,416,153, issued to Hertz et al., on Oct. 6, 1963; U.S. Pat. No. 3,878,519, issued to Eaton, on Apr. 15, 1975; and U.S. Pat. No. 4,346,387, issued to Hertz, on Aug. 24, 1982.
U.S. Pat. No. 3,709,432, issued to Robertson, on Jan. 9, 1973, discloses a method and apparatus for stimulating a filament of working fluid causing the working fluid to break up into uniformly spaced ink droplets through the use of transducers. The lengths of the filaments before they break up into ink droplets are regulated by controlling the stimulation energy supplied to the transducers, with high amplitude stimulation resulting in short filaments and low amplitudes resulting in long filaments. A flow of air is generated across the paths of the fluid at a point intermediate to the ends of the long and short filaments. The air flow affects the trajectories of the filaments before they break up into droplets more than it affects the trajectories of the ink droplets themselves. By controlling the lengths of the filaments, the trajectories of the ink droplets can be controlled, or switched from one path to another. As such, some ink droplets may be directed into a catcher while allowing other ink droplets to be applied to a receiving member.
While this method does not rely on electrostatic means to affect the trajectory of droplets it does rely on the precise control of the break off points of the filaments and the placement of the air flow intermediate to these break off points. Such a system is difficult to control and to manufacture. Furthermore, the physical separation or amount of discrimination between the two droplet paths is small further adding to the difficulty of control and manufacture.
U.S. Pat. No. 4,190,844, issued to Taylor, on Feb. 26, 1980, discloses a continuous ink jet printer having a first pneumatic deflector for deflecting non-printed ink droplets to a catcher and a second pneumatic deflector for oscillating printed ink droplets. A printhead supplies a filament of working fluid that breaks into individual ink droplets. The ink droplets are then selectively deflected by a first pneumatic deflector, a second pneumatic deflector, or both. The first pneumatic deflector is an xe2x80x9con/offxe2x80x9d or an xe2x80x9copen/closedxe2x80x9d type having a diaphram that either opens or closes a nozzle depending on one of two distinct electrical signals received from a central control unit. This determines whether the ink droplet is to be printed or non-printed. The second pneumatic deflector is a continuous type having a diaphram that varies the amount a nozzle is open depending on a varying electrical signal received the central control unit. This oscillates printed ink droplets so that characters may be printed one character at a time. If only the first pneumatic deflector is used, characters are created one line at a time, being built up by repeated traverses of the printhead.
While this method does not rely on electrostatic means to affect the trajectory of droplets it does rely on the precise control and timing of the first (xe2x80x9copen/closedxe2x80x9d) pneumatic deflector to create printed and non-printed ink droplets. Such a system is difficult to manufacture and accurately control resulting in at least the ink droplet build up discussed above. Furthermore, the physical separation or amount of discrimination between the two droplet paths is erratic due to the precise timing requirements increasing the difficulty of controlling printed and non-printed ink droplets resulting in poor ink droplet trajectory control.
Additionally, using two pneumatic deflectors complicates construction of the printhead and requires more components. The additional components and complicated structure require large spatial volumes between the printhead and the media, increasing the ink droplet trajectory distance. Increasing the distance of the droplet trajectory decreases droplet placement accuracy and affects the print image quality. Again, there is a need to minimize the distance the droplet must travel before striking the print media in order to insure high quality images. Pneumatic operation requiring the air flows to be turned on and off is necessarily slow in that an inordinate amount of time is needed to perform the mechanical actuation as well as settling any transients in the air flow.
U.S. Pat. No. 6,079,821, issued to Chwalek et al., on Jun. 27, 2000, discloses a continuous ink jet printer that uses actuation of asymmetric heaters to create individual ink droplets from a filament of working fluid and deflect thoses ink droplets. A printhead includes a pressurized ink source and an asymmetric heater operable to form printed ink droplets and non-printed ink droplets. Printed ink droplets flow along a printed ink droplet path ultimately striking a print media, while non-printed ink droplets flow along a non-printed ink droplet path ultimately striking a catcher surface. Non-printed ink droplets are recycled or disposed of through an ink removal channel formed in the catcher.
While the ink jet printer disclosed in Chwalek et al. works extremely well for its intended purpose, using a heater to create and deflect ink droplets increases the energy and power requirements of this device.
U.S. patent application entitled Printhead Having Gas Flow Ink Droplet Separation And Method Of Diverging Ink Droplets, filed concurrently herewith and commonly assigned, discloses a printing apparatus. The apparatus includes a droplet deflector system and droplet forming mechanism. During printing, a plurality of ink droplets having large and small volumes are formed in a stream. The droplet deflector system interacts with the stream of ink droplets causing individual ink droplets to separate depending on each droplets volume. Accordingly, large volume droplets can be permitted to strike a print media while small volume droplets are deflected as they travel downward and strike a catcher surface.
While the apparatus described above works extremely well for its intended purpose, images printed with large volume ink droplets typically have a lower resolution than images printed with small volume ink droplets.
It can be seen that there is a need to provide an ink jet printhead and printer of simple construction having reduced energy and power requirements capable of rendering high resolution images on a wide variety of materials using a wide variety of inks.
An object of the present invention is to simplify construction of a continuous ink jet printhead and printer.
Another object of the present invention is to reduce energy and power requirements of a continuous ink jet printhead and printer.
Yet another object of the present invention is to provide a continuous ink jet printhead and printer capable of rendering high resolution images using large volumes of ink.
Yet another object of the present invention is to provide a continuous ink jet printhead and printer capable of printing with a wide variety of inks on a wide variety of materials.
According to a feature of the present invention, an apparatus for printing an image includes a droplet forming mechanism operable in a first state to form droplets having a first volume travelling along a path and in a second state to form droplets having a plurality of other volumes travelling along the same path. Each of the plurality of other volumes being greater than the first volume. A droplet deflector system applies force to the droplets travelling along the path with the force being applied in a direction such that the droplets having the first volume diverge from the path.
According to another feature of the present invention an apparatus for printing an image includes a droplet forming mechanism operable in a first state to form printed droplets travelling along a path and in a second state to form non-printed droplets travelling along the same path. A system applies force to the printed droplets and the non-printed droplets travelling along the path with the force being applied in a direction such that the printed droplets diverge from the path and begin travelling along a printed path.
According to another feature of the present invention, a method of diverging ink droplets includes forming droplets having a first volume travelling along a path; forming droplets having a plurality of other volumes travelling along the path; and causing the droplets having the first volume to diverge from the path.